Gas distribution lines are generally comprised of high strength, rugged plastic materials such as polyethylene. Sealed joining of polyethylene lines has traditionally been accomplished by fusion involving the application of heating elements (irons) to the areas to be fused. Application of heat to the areas to be joined renders these areas in a molten state, which is followed by the application of mechanical compression for joining polyethylene network components in a sealed manner. Later approaches made use of the heat provided by an electrical conductor to fuse the polyethylene members.
This electrofusion technique permitted the cold preassembly of network components and increased fusion surfaces for stronger seals in the fabrication of larger component assemblies. Stress cracks in the thus formed seal were also reduced as were errors arising from the human element. Early fusion techniques relied heavily on the operator's experience and know-how. Relatively minor variations in heating current or heating period could result in failure of mated components to bond and form an effective seal. A general description of polyethylene fusion is provided in a publication of Trouvay & Cauvin, Inc. of Houston, Tex. entitled "INOGAZ ELECTROFUSION SYSTEM" (1987).
A seal is installed in a gas distribution line generally for the purpose of performing work on the line without shutting down the gas distribution network. Frequently a seal is installed in the distribution line when the line has been damaged and is leaking in order to seal off the leaking section and allow for its repair. Under these circumstances, time is of the essence and it is desirable to seal and repair the line as soon as possible. Current procedures in the electrofusion installation of a seal require a cooling down period following fused coupling of adjacent members. This cool down period is typically on the order of 20-25 minutes and delays initiation of repair work. This cool down period permits the polyethylene to transition from the fluid state to that of a solid in forming the seal. One example of an arrangement for the electrofusion of polyethylene pipe can be found in a brochure entitled "Stop the Flow in Plastic Pipe Without Shutdown", published by T. D. Williamson, Inc. of Tulsa, Okla., in March, 1991. Not only are prior electrofusion approaches slow, but they are also overly complicated and expensive.
The present invention addresses the aforementioned limitations of the prior art by providing an immediate, temporary seal between a distribution line and an electrofusion fitting to permit the quick insertion of a seal in the line, followed by permanent electrofusion sealing between the fitting and the line after the line is repaired. This immediate sealing of the line allows any repair work necessary to the line after it is sealed off to be quickly and easily accomplished. The electrofusion fitting is also adapted for easily and quickly connecting a branch line to the distribution line without leakage.